1. Field of the Invention
The present invention relates to a cage made of resin and more particularly to a cage made of resin suitable for a bearing which is used in a cryogenic-temperature environment in which liquid hydrogen, liquid oxygen, liquid nitrogen, LNG, and the like are used or used in a vacuum.
2. Description of Related Art
In a rolling bearing, rolling elements such as balls and cylindrical rollers are arranged in a raceway space disposed between an inner ring and an outer ring, and the rolling elements are retained by a cage. In many cases, the cage is guided at an inner-ring side or an outer-ring side. There is a case in which the rolling bearing is used in a low-temperature environment.
An angular contact ball bearing used in a rotation-supporting portion of a turbopump, of a rocket engine, which uses a liquid fuel, is a representative example of a bearing used in the low-temperature environment. FIG. 3 shows an example of the construction of an angular contact ball bearing 1 for use in the turbopump. The bearing is constructed of four kinds of component parts including an inner ring 2, an outer ring 3, a plurality of balls 4a serving as rolling elements 4, and a cage 5. The inner ring 2 and the outer ring 3 contact the balls 4a at a predetermined angle θ (contact angle) to a radial center line A. A radial load and a one-direction axial load are applicable to the bearing.
There is a case in which the bearing is used in a strict condition where the bearing is rotated at a high speed of not less than 1.6 millions in a dn value (=inner diameter (mm) of inner ring×number of rotations rpm of inner ring) in a cryogenic-temperature environment in which liquid hydrogen or liquid oxygen is present. Therefore the inner ring 2, the outer ring 3, and a plurality of the balls 4a are made of tough martensitic stainless steel, and the cage 5 is made of a composite material of polytetrafluoroethylene resin (hereinafter abbreviated as PTFE) having lubricating performance reinforced with glass fibers (non-patent document 1).
FIG. 4 shows an example of conventional cages having a pocket portion. FIG. 4(a) is a perspective view of the cage. FIG. 4(b) is a side elevation of a section D-D of FIG. 4(a). To provide a cage 5 with a pocket portion 5a, a method of forming the main body of the cage 5 of the PTFE and a method of forming the main body thereof of a metal are used.
In a known method of forming the main body of the cage 5 of the PTFE, after the cylindrically layered glass woven cloths are impregnated with the PTFE and calcined, the main body of the cage 5 and the pocket portion 5a are formed by mechanical processing, and the treatment of dissolving the glass fibers present on the surface to be processed is performed with hydrogen fluoride (patent document 1).
In a known method of forming the main body of the cage 5 of the metal, the main body of the cage 5 and the pocket portion 5a are formed by mechanical processing and the pocket member made of the PTFE is inserted into the cage (patent document 2).
In the case of the method disclosed in the patent document 1, the main body of the cage 5 is made of the composite material consisting of the sintered cylindrically layered glass woven cloths impregnated with the PTFE. Therefore the patent document 1 has a problem of (1): The material is very expensive, (2): After the material is processed into the shape of the cage, the hydrogen fluoride is required to dissolve the glass fiber present on the surface to be processed. Thus the production cost is very high, and (3): Because the method of producing the material is special, the productivity is low, and a long lead time is necessary.
In the method of the patent document 2, because the configuration of the cage is complicated, it is difficult to perform mechanical processing of the metal portion of the main body thereof.
Non-patent document 1: Masataka Nosaka, journal published by Japan Society for Composite Materials, 20 volumes, No. 6 (1994), 215-223
Patent document 1: Examined Japanese Patent Application No. 2-20854
Patent document 2: Japanese Patent Application Laid-Open No. 2003-232363